The present invention relates to a charging control circuit for an electronic wristwatch, and more particularly, to a charging control circuit, wherein for the purpose of preventing a battery from excessive charging, a charging current is by-passed so as to flow through a buzzer when an excessive charging condition is detected, for warning of the excessive charging condition.
In FIG. 1, numeral 1 designates a charging device and a solar battery is used as the charging device in the embodiment of FIG. 1. Numeral 4 designates a secondary battery which acts as a power source to supply energy to an electronic circuit 5 for a timepiece, and replenishing energy is supplied to the secondary battery from the charging device 1. A charging control circuit 3 is particularly used for preventing the battery from excessive charging.
It is well known that the battery voltage of a secondary battery under an excessive charging condition is high by a voltage of 0.2 v to 0.5 v compared with that under the normal condition. Therefore, the charging control circuit 3 is realized by the use of a voltage detecting circuit which detects the increase of voltage in the secondary battery under the excessive charging condition.
A charging current by-passing circuit 2 is controlled by an output signal from the charging control circuit 3 in such a way that the charging current producing from the device 1 is by-passed to stop the charging of the secondary battery when the secondary battery is excessively charged. Therefore, the by-passing circuit is in a non-conductive condition when the secondary battery is in a normal charging or discharging condition. A reverse flow preventing diode 6 prevents the current from flowing in a direction from the secondary battery 4 to the charging device 1 when the charging device 1 is not performing the charging function.
In the conventional circuit arranged as described above, the prevention function for excessive charging is fully performed. However, the conventional circuit can not attain high efficiency in regard to an effective use of the charging energy because the charging current is dissipated in the by-pass circuit at the time of excessive charging.